In general, in order to supply a customer with electric power, an electric power supplier sets an electricity rate for each customer based on a contract. For example, there is a contract in which a monthly maximum value of an amount of electric power per unit time (for example, 30 minutes) to be used by the customer is set as a maximum power demand and a unit price of the electricity rate is determined based on the maximum power demand. Further, depending on the electric power supplier, there is a contract in which a contract demand is set for each customer and a circuit breaker (current breaker) is activated when the electric power to be used by the customer exceeds the contract demand.
Meanwhile, social demands for energy saving, suppression of a peak of a power demand, and the like have been increasing in recent years. In particular, it is considered as a promising measure leading to reduction in environmental load to reduce the electric power to be purchased or received from the electric power supplier during a time slot in which demand for electric power increases, because high-output power plants can be reduced in number.
It is proposed to make use of a storage battery in order to prevent the unit price of the electricity rate from increasing or the circuit breaker from being activated in accordance with an increase in the power demand, and to satisfy the above-mentioned social demands. In other words, there is proposed a technology for reducing the received electric power by allowing the customer to use the storage battery and supplying the electric power from the storage battery when the power demand increases. The technology for supplying the electric power from the storage battery when there is an increase in the power demand requested by a load is known as “peak assist”.
For example, in Japanese Patent Application Laid-open No. 2006-109621, there is disclosed a technology for adjusting received electric power by controlling charging and discharging of an electric power storage system installed at an electricity customer. In Japanese Patent Application Laid-open No. 2006-109621, the received electric power is adjusted for the purpose of peak-cut for lowering the contract demand or peak-shift for reducing a usage of daytime electric power having a high unit price. Therefore, in the technology disclosed in Japanese Patent Application Laid-open No. 2006-109621, the received electric power is automatically adjusted based on a pattern set for a controller.
Incidentally, in the technology of the peak assist disclosed in Japanese Patent Application Laid-open No. 2006-109621, when the power demand at the load increases, the electric power is always supplied as long as there is room for the electric power (remaining amount) of the storage battery. This is because the customer principally aims at the peak-cut or the peak-shift.
On the other hand, from the viewpoint of achieving the reduction in the environmental load, instead of supplying the electric power from the storage battery whenever the power demand increases, it is desired to suppress the peak itself of the power demand of the customer. In other words, it is effective to reduce a frequency of peak assist by developing the customer's awareness of the suppression of the peak of the power demand. When the peak of the power demand is suppressed, a time period during which the electric power can be supplied from the storage battery is extended, and the life of the storage battery is also extended due to the reduction in the frequency of charging/discharging of the storage battery.
However, the technology disclosed in Japanese Patent Application Laid-open No. 2006-109621 is not configured to allow the customer to recognize whether or not the peak assist has been performed, and therefore has a problem in that the customer is not allowed to recognize when the power demand reaches a peak by using which load. Further, in the configuration disclosed in Japanese Patent Application Laid-open No. 2006-109621, a condition for performing the peak assist is fixed. Accordingly, the condition for performing the peak assist cannot be set so as to become proper for the customer. In other words, there is a problem in that it is not possible to enable the customer to get interested in the peak of the power demand.